This invention relates to a crop cultivation apparatus, particularly to a crop cultivation apparatus of a kind in which culture liquid is supplied from a culture liquid tank to a culture medium by virtue of gravitation and capillary phenomenon.
In the prior art, when crop cultivation is to be conducted by the use of a culture liquid, it is necessary to utilize various large scale equipments, particularly to use power equipment to periodically supply the culture liquid to a cultivation bed. Usually, in a crop cultivation system using a culture liquid, one or more pumps are used to cause the culture liquid to flow from a culture liquid tank to a cultivation bed, and then from the cultivation bed back to the culture liquid tank forming a liquid circuit therebetween. This is therefore referred to as the circulation method. Alternatively, a culture liquid is just supplied to a cultivation bed in accordance with a predetermined time interval and does not flow back. Such an operation is therefore referred to as one-way flowing method.
However, in both of the above-mentioned conventional methods, since various larger scale equipments are required and hence a house such as a glass house is needed to house these equipments, the costs for equipment purchasing and equipment installation become extremely high. Further, since an electric power supply is necessary in order to operate one or more pumps, and the pump and many other equipments need proper and periodical maintenance, another kind of cost, i.e., a cost for equipment running and maintenance might also be too large a burden for a farmer.
Moreover, in the aforesaid circulation method, since a large amount of culture liquid is required to keep a desired liquid circulation between the culture liquid tank and the cultivation bed, there often occurs a problem that a crop absorbs too much of a culture liquid or only selectively absorbs one particular component of the culture liquid, resulting in an unbalanced composition in the culture liquid. Accordingly, in order to keep various components at the desired concentrations to obtain a required composition for the culture liquid, it is necessary to check and analyze from time to time the composition of the culture liquid in the culture liquid tank and to supplement a certain component which has been found insufficient for the culture liquid.
Further, in the aforesaid one-way flowing method, although it is not necessary to periodically analyze the composition of the culture liquid in the culture liquid tank nor to supplement a certain component, it is extremely difficult to supply a correct amount of culture liquid that is exactly good for an actual consumption by the crop. In fact, the culture liquid is supplied in a much larger amount than is necessary for the actual consumption by the crop. As a result a considerable amount of the culture liquid has to be drained away from a cultivation bed, which not only causes a waste of the culture liquid but also contaminates the surrounding environment.